Abstract
57Fe Mössbauer detailed study of the spatial spin-modulated structure of the multiferroic BiFeO3 was carried out in a wide temperature range including the temperature of magnetic phase transition. The Mossbauer spectra have been analysed by fitting in terms of the anharmonic spin cycloid mode. It is established that at temperatures below ~330 K a magnetic anisotropy of the "easy axis" type is realized and above is the magnetic anisotropy of the "easy plane" type. An explanation for the change in the type of magnetic anisotropy is proposed, based on taking into account the different temperature dependences of the two contributions to the effective uniaxial magnetic anisotropy constant: a crystal anisotropy of net antiferromagnet and a weak ferromagnetism.
Highlights
The bismuth ferrite BiFeO3 is known to possess multiferroic properties, being both antiferromagnetic and ferroelectric
It was established that there existed a magnetic cycloid spiral with a long period of 620 Å incommensurate with the lattice parameter, in which G-type antiferromagnetic ordered moments of Fe atoms rotate in the direction [110]hex of wave propagation in the plane containing hexagonal symmetry axis of the rhombohedral ferrite cell
At T → 330 K, the anharmonicity parameter m → 0, which corresponds to a harmonic spatial spinmodulated structure (SSMS)
Summary
The bismuth ferrite BiFeO3 is known to possess multiferroic properties, being both antiferromagnetic and ferroelectric. It was established that there existed a magnetic cycloid spiral with a long period of 620 Å incommensurate with the lattice parameter, in which G-type antiferromagnetic ordered moments of Fe atoms rotate in the direction [110]hex of wave propagation in the plane containing hexagonal symmetry axis of the rhombohedral ferrite cell. The existence of SSMS in BiFeO3 was theoretically explained in [4, 5], where it was shown that spatial dependence of the angle θ between antiferromagnetism vector and symmetry axis on the distance x along the propagation direction, was described by the elliptic Jacobi sn-function
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